First Report of a Solar Energetic Particle Event Observed by China’s Tianwen-1 Mission in Transit to Mars
Shuai Fu, Zheyi Ding, Yongjie Zhang, Xiaoping Zhang, Cunhui Li, Gang Li, S. W. Tang, Haiyan Zhang, Yi Xu, Yuming Wang, Jingnan Guo, Lingling Zhao, Yi Wang, Xiangyu Hu, P. W. Luo, Z. Sun, Yuhong Yu, Lianghai Xie
Abstract
Abstract Solar energetic particles (SEPs) associated with flares and/or coronal mass ejection (CME)-driven shocks can impose acute radiation hazards on space explorations. To measure energetic particles in near-Mars space, the Mars Energetic Particle Analyzer (MEPA) instrument on board China's Tianwen-1 (TW-1) mission was designed. Here, we report the first MEPA measurements of the widespread SEP event occurring on 2020 November 29 when TW-1 was in transit to Mars. This event occurred when TW-1 and Earth were magnetically well connected, known as the Hohmann–Parker effect, thus offering us a rare opportunity to understand the underlying particle acceleration and transport process. Measurements from TW-1 and near-Earth spacecraft show similar double-power-law spectra and a radial dependence of the SEP peak intensities. Moreover, the decay phases of the time–intensity profiles at different locations clearly show the reservoir effect. We conclude that the double-power-law spectrum is likely generated at the acceleration site and that a small but finite cross-field diffusion is crucial to understanding the formation of the SEP reservoir phenomenon. These results provide insight into particle acceleration and transport associated with CME-driven shocks, which may contribute to the improvement of relevant physical models.